1. Technical Field
The present invention relates to a method to reduce leakage in a fourier transformer, a windowing unit adapted to reduce leakage in a fourier transformer, a fourier transformer and a discrete multi tone modem, both including such a windowing unit and a discrete fourier transform processor coupled to the windowing unit.
2. Discussion of Related Art
Such a method and equipment to perform such a method are already known in the art, e.g. from the international patent application published under the patent cooperation treaty (PCT) with reference number WO 94/21061 and with title `A multi-channel digital transmitter and receiver`. Therein, information signals are transmitted from a transmitter to a receiver, digitized in the latter one, windowed and discrete fourier transformed. As is stated on page 11, lines 14-19, spectral leakage may be reduced by increasing the window width using window functions with low sidelobes. As will be explained later on, spectral leakage causes band-limited noise to disturb all frequency components. Consequently, band-limited noise immunity may be improved by reducing spectral leakage using a window filter whose length is increased and whose head and tail are smoothed. The known solution of increasing the window width nevertheless requires an increased number of discrete fourier transform (DFT) points, and thus renders the transformation more complex.